1. Field of the Invention
The present invention relates to a voice interception system in which an ATM (Asynchronous Transfer Mode) switching system is employed to attain a mobile switching station and a voice signal is transmitted between stations under an ATM Adaptation Layer Type 2 (will be abbreviated to “AAL2” hereinafter).
2. Description of the Related Art
Conventionally, such a system is known that an ATM switching system is employed to attain a mobile switching station and a voice signal is transmitted between the stations under the AAL2. Recently, a voice CODEC (COnder-DECoder) method referred to as TFO (Tandem Free Operation) applicable to above system is released in accordance with the 3GPP (3rd Generation Partnership Project) recommendation. Thus, the advent of the voice interception system and method corresponding to that voice CODEC method has been expected.
However, conventionally, an ATM switch and an STM (Synchronous Transfer Mode) switch have been separately controlled by control software. For this reason, it is necessary to develop a CODEC peculiar to a voice monitor for converting from an ATM Adaptation Layer Type 1 for Tandem Free Operation (will be abbreviated to “AAL1 (TFO)” hereinafter) to an ATM Adaptation Layer Type 1 for reproducing the voice signal (will be abbreviated to “AAL1 (PCM)” hereinafter). Thus, it is difficult to attain the above-mentioned voice interception system.
As the related art, Japanese Laid Open Patent Application (JP-A-Heisei, 5-284560) discloses “Call Monitor System”. This call monitor system is a digital mobile communication system having a switching station for connecting between mobile stations in an original state of a low speed coding signal. In this system, the switching station includes an input signal distributor, a signal converter for converting the low speed coding signal into a PCM signal, and a call monitor. In this system, when monitoring the call between the mobile stations, the low speed coding signal sent from the mobile station is distributed by using the corresponding input signal distributor. A part of the distributed low speed coding signal is sent through a destination switching station to a destination mobile station without conversion. However, the remaining part of the distributed low speed coding signal is converted into the PCM signal by using the corresponding signal converter. Then the PCM signal is sent to the call monitor. The call monitor monitors the telephone call between the mobile stations. Accordingly, it is possible to monitor the call carried out by the low speed coding signal.
Japanese Laid Open Patent Application (JP-A-Heisei, 8-139664) discloses “Digital Signal Call Monitor”. In this digital signal call monitor, when a signal identification portion identifies a monitor signal as a non-voice mode monitor signal, converts a voice message stored in a substitution data portion into a coding voice signal, and outputs it. This outputted signal is supplied through an input switching portion and a coding mode selection portion to a decoder. The decoder converts the supplied signal into a PCM coding voice signal. Moreover, a PCM monitor circuit converts the PCM coding voice signal into an analog voice signal, and outputs it. Thus, the voice message is outputted when monitoring the non-voice mode signal. Hence, it can be evidently known that the non-voice mode signal is being monitored without any uncomfortable noise and silent tone caused by a data signal.
Japanese Laid Open Patent Application (JP-A-Heisei, 9-46288) discloses “Monitoring Method For Mobile Communication and System For The Same”. This system includes; input means which inputs a signal of a monitor channel specified by a subscriber number or a circuit number; judgment means which judges which of coding processes is carried out in accordance with the signal inputted by this input unit; and a voice signal converting means which carries out a conversion control of a voice signal in accordance with the judged result. Thus, a mobile communication system can continuously monitor communication information without initializing a channel monitor even if a coding manner is changed.
Japanese Laid Open Patent Application (JP-A-Heisei, 10-4582) discloses “Digital Signal Call Monitor”. In this digital signal call monitor, a high multiplex signal on a highway between a voice processor and a radio base station is inputted to a code conversion portion through an input terminal. The code conversion portion is provided with a time slot selection portion, a channel selection portion and a format conversion portion. A channel and a time slot to be monitored, which are specified by a channel designation portion, are selected from the above signal. The format conversion portion converts the high multiplex signal into a signal having a format on a side of a switching network of 64 Kbps. An output of the code conversion portion is connected to the input terminal for inputting a highway signal between the conventional voice processor and a switching device. Thus, in the call monitor in a digital mobile communication system represented by a digital car telephone, it is possible to carry out the voice monitor of the high multiplex signal on the highway between the voice processor and the radio base station.
Moreover, Japanese Laid Open Patent Application (JP-A-2000-78552) discloses “Television Conference System”. In this television conference system, a general-purpose personal computer is used as a television conference terminal. A decoder employs an MPEG-2 method and an encoder of a video encode server employs the MPEG-2 method. A number m of the encoders is smaller than the number n of decoders of the conference terminal. Also, they are optimized for traffic in a meeting exhibition. A multi-point conference server provides a multi-point conference service through ATM-SW to the respective terminals. The video-on demand server provides a video-on demand service to the respective terminals. Thus, it is possible to improve the initial economics when the system including the conference terminals is designed, and also possible to drop a running cost.